In the manufacture of hollow extrusions from a thermoplastic material using a continuous extrusion process, such as plastic window and door component extrusions, the extrusion exits an extruding die while still in a heated thermoplastic state. To produce a properly sized extrusion, it is necessary to calibrate the exterior profile of the hollow extrusion using a calibrator. This assures that the final extrusion has the desired exterior size and shape.
A calibrator is necessary because upon exiting the extruding die the relatively thin walls of the extrusion are soft and cannot support their own weight. Further, upon exit from the extruding die the exterior size of the extrusion sometimes varies from the desired dimension for the finished extrusion. While the extrusion is still in the plastic state, and usually immediately upon exit from the extruding die, the extrusion is passed through one or more calibrators which apply a vacuum to the thin walls of the extrusion to pull them against the interior walls of an elongated calibrating aperture which has the desired size and shape (i.e., the exterior profile) of the finished extrusion. This prevents the relatively thin walls of the extrusion from sagging or otherwise deforming as the extrusion is pulled through the calibrator.
While the vacuum holds the walls of the extrusion in place against the interior walls of the calibrating aperture as the extrusion moves through the calibrator, cooling water is typically passed through channels in the calibrator to conduct heat away from and thereby cool the extrusion until it is sufficiently rigid that it will maintain the desired size and shape of the finished extrusion upon its exit from the calibrator. Since the extrusion takes time to cool and the production through-put requirement is relatively large in most applications, several calibrators must sometimes be used in series so that when the extrusion exits the last calibrator it will have cooled sufficiently to maintain its own size and shape without the support of the vacuum. Eventually, the extrusion reaches a cutter, and the extrusion is cut to the desired length. Such calibrators are shown in various U.S. patents such as, U.S. Pat. Nos. 4,468,369; 4,120,926 and 4,401,424, incorporated herein by reference.
Typically, prior art calibrators have been formed as an integral unit from aluminum or stainless steel, or some other heat conductive material. The heat of the extrusion, while still in the plastic state, is conducted through the metal walls of the calibrator to water circulating through water channels that have been cut in the metal walls. The cooling of the plastic occurs while it is being pulled through the calibrator with its thin walls held in position by the vacuum being applied through a series of vacuum apertures also cut into the metal walls of the calibrator. Hoses are connected to ports in the metal walls to handle the supply and return of the cooling water between the water channels and an external source of water, and to make the connection of the vacuum apertures to an external source of vacuum.
In the past, an entirely new calibrator had to be machined for each specific extrusion profile being produced. As shown in U.S. Pat. Nos. 4,120,926 and 4,468,369, vacuum calibrators have typically been made from several thick metal slabs that have been machined to match the profile of the extrusion being manufactured, to incorporate the water channels for cooling the extrusion, and to incorporate the vacuum apertures which apply the vacuum to the extrusion walls as they pass by the vacuum apertures. The slabs are individually machined and then assembled to form the calibrator. If it was desired to change the profile slightly, or it was desired to produce a new profile using the same production line equipment, it was necessary to machine a completely new calibrator, remove the old one from the production line, and replace it with the new calibrator. When replacing an existing calibrator in the production line with a new calibrator, the production line had to be closed down for a substantial period of time until the new calibrator could be put in position and aligned with the extrusion die, and the vacuum and water supplies reconnected to the new calibrator. This is an expensive, time consuming process. Further, the machining of the extrusion profile and the water channels and vacuum apertures into the metal slabs took time and was quite expensive. The same problems were encountered when it was necessary to replace a calibrator which has been worn to the point of providing insufficient tolerance for the extrusion, or to remove the calibrator for cleaning.
An alternative prior art calibrator design is shown in U.S. Pat. No. 4,401,424. This calibrator includes a plurality of pairs of upper and lower sizing elements, with each pair of sizing elements being shaped to define therebetween a longitudinal portion of the calibrating aperture. The pairs of sizing elements are disposed end to end so that together they define the entire calibrating aperture through which the heated extrusion passes. Upper and lower backing members are disposed, respectively, above and below the pairs of sizing elements and extend over the entire length of the calibrator. The upper and lower backing members are releasably secured together with the pairs of upper and lower sizing elements positioned therebetween to clamp the sizing elements in place to define the calibrating aperture. Each of the sizing elements has a vacuum chamber or manifold formed therewithin and slits and bore holes which communicate vacuum from the vacuum manifold to the extrusion as it passes through the calibrating aperture. The vacuum is supplied from an external source of vacuum. Each of the sizing elements also has a cooling water chamber formed therein which is connected to an external source of cooling water. Vacuum and water hoses are connected directly to each of the upper and lower sizing elements of each of the pairs of sizing elements which together form the calibrator.